McCune-Albright Syndrome (MAS) was originally described as the triad of polyostotic fibrous dysplasia of bone, cafe-au-lait skin pigmentation and precocious puberty. Other endocrine abnormalities have been identified in this disease. Growth hormone (GH) excess is associated with MAS and occurs in approximately 10% of the patients. Current therapies of MAS involve separate treatment for the bone and endocrine diseases. We propose to test the effectiveness of a novel GH receptor antagonist, pegvisomant at reducing the growth hormone excess in these patients. Secondarily we shall also assess the impact of pegvisomant therapy on the fibrous dysplastic bone lesions associated with the disease.